Printing drum and method for producing same

Abstract: A printing drum mounted rotatably in a printing machine, the printing drum including an ink-permeable peripheral wall (1), with ink being feedable from the inside of the ink-permeable peripheral wall (1), and an ink-permeable screen (4) formed of a heat-shrinkable material and held in a heat-shrinkable manner in close contact with the outer peripheral surface of the ink-permeable peripheral wall (1).

Description: The present invention relates to a printing drum to be mounted in a printing machine such as, for example, a mimeographing machine, as well as a method for producing the same. Fig. 4 illustrates a conventional printing drum 10 mounted in a mimeographing machine. The printing drum 10 has a cylindrical, peripheral wall 1 in which there are formed a large number of fine holes for the passage of ink therethrough. Inside the peripheral wall 1 is disposed an ink feeder though not shown. On the outer peripheral surface of the cylindrical, peripheral wall 1 is provided a stencil clamping means 2 in parallel with the axis of the peripheral wall 1. Further, two ink-permeable screens 11 and 12 are wound one upon the other round the outer peripheral surface of the peripheral wall 1. The screens 11 and 12 are for dispersing the ink which has passed through the fine holes of the peripheral wall 1 uniformly throughout the whole of the printing area on the printing drum and also function to hold an appropriate amount of the ink to make clear and uniform printing possible. The screen 11 as an inner screen is of a relatively large mesh, while the screen 12 as an outer screen is of a relatively small mesh. One end portions of both screens 11 and 12 are fixed to the clamp means 2 with bolts 13 or the like. The screens 11 and 12 are put one upon the other and wound round the peripheral wall 1. The opposite end portions of both screens 11 and 12 are provided with elongated strip-like edge members 14 and 15, respectively. As shown in Fig. 5, both side portions of the edge members 14 and 15 are connected together by means of clip members 16. The edge members 14 and 15 thus rendered integral with each other are then mounted to the clamp means 2 through springs 17, as shown in Fig. 6. Both screens 11 and 12 are brought into close contact with the outer peripheral surface of the peripheral wall 1 by the biasing force of the springs 17. For performing the operation of winding the screens 11 and 12 round the peripheral wall 1 and then fixing them with springs 17 the printing drum 10 is fixed onto a fixing jig 20, as shown in Fig. 4. According to the conventional printing drum 10 described above, there has been the problem that the construction for mounting the screens 11 and 12 onto the peripheral wall 1 is complicated, the number of components is large, and it is necessary to provide a special jig. Further, since the springs 17 have a strong biasing force, if they are not securely mounted in the spring mounting operation, they may be disengaged and cause an accident of injury. Thus there has been the problem that the drum assembling work involves danger. It is the object of the present invention to bring an ink-permeable screen into close contact with the outer peripheral surface of the printing drum peripheral wall, using an extremely simple and safe construction. DATABASE WPI Week 7320, Derwent Publication Ltd, London, GB; AN 73-28691U & JP-A-48 015 240 (UENOYAMA KIKO) dicloses a method of producing cylindrical screen stencils which comprises (1) covering a nickel cylindrical screen with a tubular cloth produced by circular-knitting or hollow weaving of thread made of heat-shrinkable synthetic fibres; (2) heat-shrinking the tubular cloth to attain a tight contact between the cloth and the cylinder, and (3) developing patterns on the cloth by means of known photo-engraving process for screen stencils. Clear-cut patterns can be obtained because of higher screen-mesh (100-150 mesh can be obtained in the heat-shrunk screen), and even very fine lines of half-tones can be reproduced. The present invention is as claimed in the claims. Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a perspective view illustrating a printing drum and useful for understanding the present invention; Fig. 2 is a partially enlarged view illustrating a principal portion of a first embodiment of the present invention; Fig. 3 is a perspective view illustrating a second embodiment of the present invention; Fig. 4 is a perspective view of a conventional printing drum; Fig. 5 is a view illustrating a screen mounting structure in the conventional printing drum; and Fig. 6 is a view illustrating a screen mounting structure in the conventional printing drum. Fig. 1 illustrates a printing drum 3 which is not according to the present invention. In the printing drum 3, such components as peripheral wall 1, clamp means 2 and ink feeder (not shown) are of the same constructions as in the conventional printing drum 10 described above. In Fig. 1, the components each common to any of those shown in Fig. 4 are indicated by the same reference numerals as in Fig. 4 and explanations thereof will be omitted. In Fig. 1, two ink-permeable screens 4 and 5 formed of a heat-shrinkable material, e.g. polyester, are mounted one upon the other around the outer peripheral surface of the peripheral wall 1. The screens 4 and 5 have each been prepared by processing a polyester sheet into mesh form to permit the passage of ink therethrough and then vapor-depositing stainless steel thereon. The screen 4, which is positioned inside is of a relatively large mesh, while the screen 5, which is located outside, is of a relatively small mesh. Reference will now be made to the procedure for mounting both screens 4 and 5 to the peripheral wall 1. First, end portions 4a and 5a of the screens 4 and 5 are put one upon the other, arranged in order, and fixed to a portion of the peripheral wall 1 adjacent to one edge portion 2a of the clamp means 2 by means of a fixing sheet 6. The fixing sheet 6 comprises a long paper strip-like polyester film and an adhesive layer formed on one side of the film. With a single sheet 6, end portions 4a and 5b of both screens 4 and 5 are fixed. The screens 4 and 5 thus put one upon the other are wound round the peripheral wall 1, and an opposite end portion 5b of the outer screen 5 is fixed to the peripheral wall 1 by means of another fixing sheet 7. The opposite end portion 5b of the outer screen 5 is fixed to a portion of the peripheral wall 1 adjacent to an opposite edge portion 2b of the clamp means 2. An opposite end portion 4b of the inner screen 4 is not directly fixed but is held in place between the outer screen 5 and the peripheral wall 1. Next, both screens 4 and 5 are heated. As heating means, one capable of heating both screens as uniformly as possible is preferred such as, for example, warm air, hot water or light. The screens 4 and 5 thus heated shrink, particularly to a greater extent in the circumferential direction than in the axial direction. Although both screens 4 and 5 are formed of the same material, they are different in the percent heat shrinkage because they are of different mesh sizes. The inner screen 4 of a larger mesh is relatively small in the percent heat shrinkage and is difficult to shrink, while the outer screen 5 of a smaller mesh is relatively large in the percent heat shrinkage and is easy to shrink. Since the outer screen 5 is large in the percent heat shrinkage and both its end portions 5a and 5b are fixed to the peripheral wall 1, a suitable tension is generated, thus causing the screen 5 to come into close contact with the peripheral wall 1. Although the inner screen 4 is fixed only at its one end portion 4a, the opposite end portion 4b thereof is sufficiently held in place by the pressing action of the outer screen 5 because the percent heat shrinkage thereof is relatively small. That is, the inner screen is fixed to the peripheral wall 1 by virtue of one fixing sheet 6 and the outer screen 5, and an appropriate tension is generated in the inner screen upon heat shrinkage thereof, whereby the inner screen is brought into close contact with the peripheral wall 1. The fixing sheet 6 also possesses the function as a protective sheet which protects an end portion of the screen 5. As the sheet 6 there may be used, for example, a thin sheet of a polycarbonate or a metal. For using the printing drum 3 of this embodiment, a stencil after process work is wound round the outer peripheral surface of the outer screen 5 and one end thereof is fixed by the clamp means 2. Then, the printing drum 3 is rotated while ink is fed from the inside of the peripheral wall 1, and paper is fed to the drum 3. The paper is held between the outer peripheral surface of the printing drum 3 and an urging means (not shown) disposed outside the drum 3, and in this state the paper is conveyed and printed. Although this embodiment relates to mimeograph, the present invention is also applicable to other printing means using a printing drum. Although two screens are used, the number of screen may be one or three or more. The screen end fixing method is not limited to the use of an adhesive tape. There may be adopted any other simple method, for example the use of bolts or the like. Further, as to which portion of the screen is to be fixed to the drum peripheral wall, this can be determined while taking into account what tension will be generated in the screen when heated. If at least both ends in the circumferential direction are fixed as in this embodiment, it is possible to obtain a required tension in the circumferential direction. The first embodiment of the present invention will be described below with reference to Fig. 2. The printing drum of this embodiment is the same as that of Figure 1 in point of the construction of an ink-permeable peripheral wall and that of ink feed means disposed inside the peripheral wall. This first embodiment of the present invention finds its feature in the screen used and also in the screen mounting structure for the peripheral wall. A screen 30 in this embodiment illustrated in Fig. 2 is wound round an ink-permeable peripheral wall (not shown) of the printing drum. Although the screen 30 is ink-permeable, it is not always required to be heat-shrinkable. Opposed end portions 30a and 30a of the screen 30 thus wound round the drum peripheral wall are connected with each other by means of a long fixing member 31 formed of a heat-shrinkable material. In each of the end portions 30a and 30a of the screen 30 are formed a plurality of holes 32 at predetermined intervals, and the long fixing member 31 is passed alternately through the holes in both end portions 30a and 30a to connect both end portions with each other. Now, heat is applied to the fixing member 31 to cause shrinkage of the same member, whereby both end portions 30a and 30a of the screen 30 interconnected by the fixing member 31 are pulled toward each other, and hence the screen 30 comes into close contact with the drum peripheral wall. Next, a second embodiment of the present invention will be described below with reference to Fig. 3. The printing drum of this embodiment is the same as in that of Figure 1 in point of the construction of an ink-permeable peripheral wall and that of ink feed means disposed inside the peripheral wall. This embodiment is characteristic in both screen 40 and a screen mounting structure for the peripheral wall. The screen in this embodiment illustrated in Fig. 3 is wound round an ink-permeable peripheral wall 1 of the printing drum. Although the screen 40 is permeable to ink, it is not always required to be heat-shrinkable. One rectangular fixing member 41 formed of a heat-shrinkable material is bonded through an adhesive to opposed, both end portions 40a and 40a of the screen 40 wound round the peripheral wall 1. Both end portions 40a and 40a are interconnected by the fixing member 41. When heat is applied to the fixing member 41, thereby causing the fixing member to shrink, both end portions 40a and 40a of the screen 40 interconnected by the fixing member 41 are pulled toward each other and the screen 40 is thereby brought into close contact with the outer peripheral surface of the peripheral wall 1. In the first and second embodiments described above, since tension is applied to the screens 30 and 40 using the heat-shrinkable fixing members 31 and 41, the screens themselves are not always required to be heat-shrinkable. However, if not only there is used a heat-shrinkable fixing member but also each screen is constituted using a heat-shrinkable material, then by adjusting the fixing position of the two and the length of the fixed portion, there can be obtained the effect that the direction and magnitude of tension to be generated in the screen can be suitably set more easily in accordance with the object to be achieved. Although in the foregoing first and second embodiments both end portions of the screens 30 and 40 each wound round the peripheral wall are interconnected by the heat-shrinkable fixing members 31 and 41, respectively, there are other constructions which may be adopted for imparting tension to each screen through a heat-shrinkable member provided separately from the screen. For example, according to one such construction, one end of the drum screen wound round the peripheral wall is fixed to the drum peripheral wall using a heat-shrinkable fixing member, while the opposite end thereof is fixed to the peripheral wall using another means. Then, upon heat-shrinkage of the fixing member, the screen is pulled and comes into close contact with the peripheral wall. According to another construction, both ends of the screen respectively wound round the drum peripheral wall are fixed respectively to the peripheral wall using two, heat-shrinkable, fixing members. Then, upon heat-shrinkage of both fixing members, the screen is pulled and comes into close contact with the peripheral wall. According to the present invention, an ink-permeable film can be positively loaded onto the peripheral wall of a printing drum using an extremely simple construction and process with reduced number of components. Besides, since it is not necessary to use a spring for the mounting of screen, the safety of the printing drum assembling work is improved.

Claims: A printing drum for mounting rotatably in a printing machine, said printing drum including: an ink-permeable peripheral wall (1) with ink being feedable from the inside of said peripheral wall (1) to effect printing; and an ink-permeable screen (30) wound round the outer peripheral surface of said peripheral wall (1) with a stencil wound round said ink-permeable screen (30); characterised in that: a fixing means (31) formed of a heat-shrinkable material connects both end portions (30a,30a) of said screen (30) with each other and, by its own heat-shrinkage, holds the screen (30) in close contact with said peripheral wall (1). A printing drum for mounting rotatably in a printing machine, said printing drum including: an ink-permeable peripheral wall (1) with ink being feedable from the inside of said peripheral wall (1) to effect printing; and an ink-permeable screen (40) wound round the outer peripheral surface of said peripheral wall (1) with a stencil wound round said ink-permeable screen (40); characterised in that: a fixing means (41) formed of a heat-shrinkable material fixes at least one end portion (40a) of said screen (40) to said peripheral wall (1) and, by its own heat-shrinkage, holds the screen (40) in close contact with said peripheral wall (1). A method for producing a printing drum to be mounted rotatably in a printing machine, said printing drum including: an ink-permeable peripheral wall (1) with ink being feedable from the inside of said peripheral wall to effect printing; and an ink-permeable screen wound round the outer peripheral surface of said peripheral wall (1) with a stencil wound round said peripheral wall (1) characterised in that: the method comprises the steps of winding said screen (30,40) round the outer peripheral surface of said peripheral wall (1), said ink-permeable screen connecting both end portions (30a,40a) of said screen (30,40) by a fixing means (31,41) formed of a heat shrinkable material and thereafter causing said fixing means (31,41) to shrink thermally, thereby causing the screen (30,40) to come into close contact with said peripheral wall (1).

Inventors: KAWABE TAKAO, KAWABE, TAKAO
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1994
Main classification: B41L13
IPC codes: B41L13